Various automotive vehicles have recently begun including vehicle dynamic control systems. Such vehicle dynamic control systems include yaw stability control systems, roll stability control systems, integrated vehicle dynamic control systems, etc. The ongoing goal of vehicle controls is to achieve a coordinated system level vehicle performances for ride, handling, safety and fuel economy.
With current advances in mechatronics, vehicle controls have increased opportunities for achieving performances, which were previously reserved for spacecraft and aircraft. For example, gyro sensors, previously only used in aircraft, have now been incorporated in various vehicle controls, and the anti-lock brake systems invented for airplanes are now standard automotive control systems. Current sensor technology generates ever-increasing opportunities for vehicle control. A typical vehicle control system senses 3-dimensional dynamic vehicle motions. For example, during yaw stability and roll stability controls, the control task involves three-dimensional motions along the vehicle roll, pitch, and yaw directions and along the vehicle longitudinal, lateral and vertical directions.
The coupling between different motion directions may not be as strong as in an aircraft or a spacecraft, however, they cannot be neglected in most maneuvers that involve vehicle rolling over or yawing. For example, the excessive steering of a vehicle will lead to excessive yaw and lateral motion, which further cause large rolling motion towards the outside of the turning. If the driver brakes the vehicle during the excessive steering, then the vehicle will also experience roll and pitch motions together with lateral and longitudinal accelerations. Hence, a successful vehicle dynamics control involves an accurate determination of the vehicle roll, pitch and relative yaw attitude (same as the so-called sideslip angle).
With the aforementioned vehicle attitude determination needs, a new vehicle sensing technology which contains an inertial measurement unit (IMU) and all the other sensors used in vehicle controls is desirable. This sensing system is called an Integrated Sensing System (short to ISS). IMUs have been used in inertial navigation system (INS) for aircraft and satellite for decades. Typically an INS system determines the attitude of a flight vehicle through the sensor signals from the IMU sensors. The IMU sensor set includes three gyros and three linear accelerometers. The INS contains an IMU and a processor unit to compute the navigation solutions necessary for navigation, attitude reference and various other data communication sources. At the same token, the ISS will also be used (but not limited) to vehicle attitude determination.
With the use of IMU sensor cluster and the other standard sensors equipped with a vehicle, accurate estimation of the vehicle operating states is possible. One of the important states are the forces and torques applied to the wheels, including tire longitudinal and lateral forces, the driving torques and braking torques applied to the wheels. Those torques and forces may be used to determine the intention of the driver, the road surface condition and to facilitate the vehicle dynamics controls like yaw stability control and roll stability control. A four-wheel model is used in the computation rather than a bicycle model in prior known systems. This results in a more accurate determination of the forces and torques. Existing computations of the tire lateral forces using a bicycle model are conducted along the vehicle body frame; hence normal loading will contaminate the computation. The bicycle model also cannot differentiate vehicle yaw motion due to longitudinal force deviation between the left and right sides and is inaccurate during brake intervention.
It would therefore be desirable to accurately estimate the tire lateral and longitudinal forces applied to the wheels, and the braking and driving torques applied to each wheel.